A ball is thrown upward and allow to fall under the influence of gravity. We wil

Question

A ball is thrown upward and allow to fall under the influence of gravity. We will ignore the effects of air resistance. We consider three times: Time A, when the ball is first thrown upward, Time B, when the ball reaches the peak of its motion, and Time C, when the ball hits the ground. Rank the power delivered by the gravitational force to the ball at those three times from least to greatest.

a. A = B = C

b. B < A = C

c. A = C < B

d. A < B < C

e. C < B < A

f. Insufficient information to determine the correct answer.

PROVE YOUR ANSWER IS RIGHT OR NO POINTS

Explanation / Answer

The simplest way to think about it, is to realize that in a situation like this, in which the force constant and always parallel to the displacement, the work done is the force times the distance.

But as the object falls, it speeds up, so in any given unit of time (for example, one second), the displacement is greater the longer the object has been falling. So, as the force doesn't change, the longer an object has been falling, the more work is done in a given time. Since power is the time rate of energy transformation (time rate of work done, in this case), if more work is being done in a given time, the power is greater.

so the answer is option d) A < B < C

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